Doppler Frequency Shift

    As satellites move across the sky in relation to the ground level viewer, the signals from the satellite and to the satellite change in freqeuncy. When the satellite is coming toward you the frequency of the downlink will be recieved slightly higher in frequency and the reverse is true when the satellite is moving away. Technically, your uplink should be tuned in an inverse relation with the downlink frequency. However, AO-27 has a slightly wide reciever, so that most users just leave their transmit frequency on 145.85. The downlink needs to be tuned during the pass. Typically, I've received the satellite at 436.8 at the start of a pass and have to tune down in .005 megahertz steps. This seldom goes below 436.780 in frequency. However, you can lose the satellite due to this in the middle of a QSO only to find your party calling you clearly on the next increment down in frequency.
    This can be a little disconcerting at first, especially if you are also hand-tracking the satellite. I can hold my current hand-held and still turn the tuning knob with the same hand. If you can write with a pen in your teeth, and talk at the same time,  you can copy down your log information. I generally stick a small VOX tape recorder in my pocket to record possible logs.

A Problem Unrelated to Doppler

     Once your neighbors see you in the back yard waving an antenna back and forth, they may call the police or the nearest mental institution. If you tell them you're talking to someone on a small, quickly moving satellite, they'll commit you immediately.
     I recommend hanging several shirts over the Arrow antenna. It then looks like your trying to speed up the drying of some laundry, while talking on your cellphone. The neighbors won't blink an eye.....

The Challenge of Operating AO-27

     Since it is basically just a FM repeater, only one station can transmit at a time. This makes the short pass time a challenge, since there are many users waiting to use the satellite at any given pass. For a beginner like myself, this is particularly challenging. You must politely wait while other QSO's go on. When when QSO signs off, there is usually a deluge of stations calling either CQ or particular calls for a scheduled QSO. If you can arrange a "sked" it will make the likelyhood of a contact much higher.
     There have been many many satellite passes where all I get to do is listen.  It takes patience, but one must be ready to announce your call quickly. This isn't easy for a beginner like myself. As will be stressed later, it is important to never transmit unless you can clearly hear the satellite.  You may have simply lost the downlink due to doppler and your transmission will be covering up someone elses QSO. Weekday passes are considerably easier to work, since less hams are trying to make a contact.